The present invention relates generally to the field of hydraulic circuits utilized in automatic transmission systems and, more particularly, to a Self-Regulating Reverse Boost Valve for use in General Motors 4L80E transmissions.
Automatic transmission systems of the prior art have a hydraulic circuit sub-system, which includes at least a hydraulic pump, a valve body having fluid conducting passages or circuits, input and exhaust ports formed within the fluid circuits, and a plurality of spool valves so-called because of their resemblance to sewing-thread type spools. Such valves are comprised of generally cylindrical pistons having control diameters or lands formed thereon, which alternately open and close the ports to the fluid circuits to regulate the flow and pressure of automatic transmission fluid (hereinafter xe2x80x9cATFxe2x80x9d) in order to actuate different components of the transmission. It will be understood that in describing hydraulic circuits, ATF usually changes names when it passes through an orifice or control valve in a specific fluid circuit.
In the General Motors (hereinafter xe2x80x9cGMxe2x80x9d) 4L80E transmission the Reverse Boost Valve is activated by Torque Signal (hereinafter xe2x80x9cTSxe2x80x9d) fluid pressure from the Variable Force motor and operates against the force of the Pressure Regulator valve spring. Such TS fluid pressure induced movement forces the Pressure Regulator valve to move against ATF supply from the hydraulic pump thereby boosting line pressure in relation to engine torque. When Reverse gear range is selected, reverse fluid pressure also forces the Reverse Boost valve to move toward the Pressure Regulator valve to boost line pressure.
Common service problems in the GM 4L80E transmission are an uncontrollable rise in main line hydraulic pressure (i.e. upwards of 500-600 psi), high line pressure in Reverse gear, broken direct clutch drums, and/or broken cases, which result from excessive Torque Signal pressure leaking past the original equipment manufacture (hereinafter xe2x80x9cOEMxe2x80x9d) Boost Valve and into the Reverse fluid circuit. Thus, the present invention has been developed to resolve this problem and other shortcomings of the prior art.
Accordingly, the present invention is a Self-Regulating Reverse Boost Valve Assembly for an automatic transmission such as the GM 4L80E transmission including an internal check valve mechanism that is actuated whenever Torque Signal pressure to the present Reverse Boost Valve Assembly exceeds a predetermined level (i.e. 95-100 psi). The excess ATF pressure is diverted to fluid exhaust circuits via an internal fluid channel formed in the present valve to the transmission sump. In this manner excessive main line pressure, excessive line pressure in Reverse gear, broken direct clutch drums, and/or damaged transmission cases are avoided.
Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings.